Capacitors having doped aluminum oxide dielectrics

ABSTRACT

Doped aluminum oxide layers having a porous aluminum oxide layer and methods of their fabrication. The porous aluminum oxide layer may be formed by evaporation physical vapor deposition techniques to facilitate formation of a high-purity aluminum oxide layer. A dopant material is embedded in the pores of the porous aluminum oxide layer and subsequently converted to a dielectric form. The degree of porosity of the porous aluminum oxide layer may be controlled during formation to facilitate control of the level of doping of the doped aluminum oxide layer. Such doped aluminum oxide layers are useful as gate dielectric layers, intergate dielectric layers and capacitor dielectric layers in various integrated circuit devices.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/808,189 (published) filed Mar. 24, 2004 and titled, “DOPED ALUMINUMOXIDE DIELECTRICS,” which is a continuation of U.S. patent applicationSer. No. 09/792,777 filed Feb. 23, 2001 and titled, “DOPED ALUMINUMOXIDE DIELECTRICS,” now U.S. Pat. No. 6,858,865 issued Feb. 22, 2005,each of which is commonly assigned and incorporated by reference in itsentirety herein.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to dielectrics for integratedcircuit devices, and in particular to the development of doped aluminumoxide dielectrics and devices containing such dielectrics.

BACKGROUND OF THE INVENTION

To meet demands for faster processors and higher capacity memories,integrated circuit (IC) designers are focusing on decreasing the minimumfeature size within integrated circuits. By minimizing the feature sizewithin an integrated circuit, device density on an individual chipincreases exponentially, as desired, enabling designers to meet thedemands imposed on them. As modem silicon devices become smaller and theminimum feature size of CMOS (complementary metal oxide semiconductor)devices approaches and goes below the 0.1 μm regime, very thin gateinsulators of thickness less than 2 nm (20 Å) will be required to keepthe capacitance of the DRAM (dynamic random access memory) capacitorcell in the range of 30 fF. This capacitance value is generally requiredto provide immunity to radiation, soft errors and a nominalsignal-to-noise ratio.

Silicon dioxide (SiO₂), the most commonly used insulator, shows highleakage current density at thicknesses in the range of 20 nm due toband-to-band tunneling current or Fowler-Nordheim tunneling current. Asa result, high-k dielectric films such as aluminum oxide (Al₂O₃),tantalum pentoxide (Ta₂O₅) and titanium dioxide (TiO₂) have receivedconsiderable interest as gate insulators to replace silicon dioxide.

While aluminum oxide has shown considerable promise, its porous natureleads to drawbacks. It has been noted that aluminum oxide porosity isgenerally the result of an acicular crystalline structure and that somepores may extend through the entire thickness of an aluminum oxide layerhaving a thickness on the order of 100 nm. Studies have also shown thatexposure to humid atmospheres and even normal atmospheric conditionsleads to a build-up of water in the pores of aluminum oxide films. Thiswater build-up results in a loss of dielectric properties. Inparticular, water build-up can lead to a decrease in breakdown voltageof several orders of magnitude.

For the reasons stated above, and for other reasons stated below thatwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foralternative aluminum oxide structures and methods of their production.

SUMMARY

Aluminum oxide has shown considerable promise as a dielectric materialfor integrated circuit devices. However, its porous nature leads todrawbacks, in that the pores can adsorb water, thus resulting in adetrimental impact on the dielectric properties of the aluminum oxidematerial. The various embodiments of the invention involve a porousaluminum oxide layer having dopant material embedded in its pores andsubsequently converted to a dielectric form. The doped aluminum oxidelayer is formed sequentially to facilitate formation of a high-purityaluminum oxide layer and subsequently sealing its pores to impede wateradsorption. Doped aluminum oxide layers of various embodiments areespecially suited for use as gate dielectric layers, intergatedielectric layers and capacitor dielectric layers in various integratedcircuit devices.

For one embodiment, the invention provides a capacitor. The capacitorincludes a first capacitor plate, a second capacitor plate and adielectric layer interposed between the first capacitor plate and thesecond capacitor plate. The dielectric layer includes an aluminum oxidelayer and a second dielectric material embedded in a surface of thealuminum oxide layer. A dopant material is embedded in the surface ofthe aluminum oxide layer after a formation of the aluminum oxide layer,thereby not dispersing the dopant material throughout the aluminum oxidelayer. The dopant material of silicon, zirconium, hafnium and/ortitanium is subsequently treated to form the second dielectric material.

For another embodiment, the invention provides a capacitor. Thecapacitor includes a first capacitor plate, a second capacitor plate anda dielectric layer interposed between the first capacitor plate and thesecond capacitor plate. The dielectric layer includes an aluminum oxidelayer and a second dielectric material embedded in a surface of thealuminum oxide layer. A degree of porosity of the aluminum oxide layeris controlled during formation of the aluminum oxide layer. A dopantmaterial is then embedded in the surface of the aluminum oxide layerafter a formation of the aluminum oxide layer, thereby not dispersingthe dopant material throughout the aluminum oxide layer. The dopantmaterial is silicon, zirconium, hafnium or titanium. The dopant materialis subsequently treated to form the second dielectric material ofsilicon dioxide, zirconium dioxide, hafnium dioxide, titanium dioxide orsilicon nitride.

Further embodiments of the invention include apparatus of varying scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are cross-sectional views of a doped aluminum oxide layertaken during various processing stages in accordance with an embodimentof the invention.

FIG. 1D is a cross-sectional view of one deposition system for use informing the aluminum oxide layer of FIGS. 1A-1C.

FIG. 2 is a cross-sectional view of a field-effect transistor inaccordance with an embodiment of the invention.

FIG. 3 is a cross-sectional view of a floating-gate field-effecttransistor in accordance with an embodiment of the invention.

FIG. 4 is a cross-sectional view of a portion of a DRAM memory array inaccordance with an embodiment of the invention.

FIG. 5 is a simplified block diagram of an integrated circuit memorydevice in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the present embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process, electrical or mechanical changes may be madewithout departing from the scope of the present invention. The termswafer or substrate used in the following description include any basesemiconductor structure. Examples include silicon-on-sapphire (SOS)technology, silicon-on-insulator (SOI) technology, thin film transistor(TFT) technology, doped and undoped semiconductors, epitaxial layers ofa silicon supported by a base semiconductor structure, as well as othersemiconductor structures well known to one skilled in the art.Furthermore, when reference is made to a wafer or substrate in thefollowing description, previous process steps may have been utilized toform regions/junctions in the base semiconductor structure, and theterms wafer and substrate include the underlying layers containing suchregions/junctions. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined only by the appended claims and equivalents thereof.

FIGS. 1A-1C depict fabrication of a doped aluminum oxide layer 108 as aportion of an integrated circuit device in accordance with oneembodiment of the invention. FIGS. 1A-1C are cross-sectional views takenduring various processing stages.

In FIG. 1A an aluminum oxide layer 102 is formed on the substrate 100.The aluminum oxide layer 102 is porous, containing one or more pores 104on the surface. Note that pores 104 may extend through the aluminumoxide layer 102 to the substrate 100 such as pore 104 a. Voids 103 maybe contained in the aluminum oxide layer 102. Voids 103 are spacesbetween grains or crystals of aluminum oxide that do not extend to thesurface of the aluminum oxide layer 102.

The substrate 100 may be a monocrystalline silicon material. Forexample, the substrate 100 may be a wafer of monocrystalline siliconhaving a [100] orientation. The substrate 100 is generally asemiconductor material doped to a conductivity type, such as a p-typeconductivity. As an example, the substrate 100 may be implanted with ap-type dopant, such as boron, followed by an anneal to produce a p-typesubstrate. As another example, the substrate 100 may have an n-typeconductivity, such as a silicon substrate doped using an n-type dopantsuch as phosphorus or arsenic. Alternatively, the substrate 100 may besome other layer of an integrated circuit device. For example, thesubstrate 100 may be a floating gate layer of a floating-gatefield-effect transistor. The substrate 100 may further include othersemiconductor, conductor or insulator layers.

The aluminum oxide layer 102 is formed through physical vapor deposition(PVD) techniques to produce a high-purity film. The PVD techniquespreferably are evaporation techniques using a high-purity aluminum oralumina source, such as zone-refined aluminum or sapphire crystals. Suchsources are significantly more pure than traditional powder targetscommonly used in PVD sputtering techniques. For one embodiment, thealuminum or alumina source has a purity in excess of 99.99%. For afurther embodiment, the aluminum or alumina source has a purity ofapproximately 99.9999%. Evaporation PVD techniques are well understoodin the art. Examples include thermal evaporation, electron-beamevaporation and ion-beam-assisted deposition. For aluminum sources,formation of an aluminum oxide layer 102 would require reactiveevaporation of the aluminum source in an oxygen-containing atmosphere, atechnique well known in the art.

The level of porosity of the aluminum oxide layer 102 may be expressedas packing density. Packing density, p, is a measure of the extentindividual grains or crystals of aluminum oxide occupy the gross volumeof the aluminum oxide layer 102 relative to voids or pores. Packingdensity has been defined in literature by the relation:p=σ/ρ_(sc) h)

where:

-   -   σ is the surface density of the layer;    -   ρ_(sc) is the volume density of the skeleton of the film; and    -   h is the geometric height of the film        As a first approximation, ρ_(sc) can be equated to the density        of sapphire, or 3.99 g/cm³.

Wide ranges of packing density are readily producible in aluminum oxidefilms as has been reported in the literature. See, e.g., Brik, E. B.,“Effect of Substrate Temperature on Density of Aluminum Oxide Films,”Opt. Mekh. Promst. 57 (1), pp. 50-52 (January 1990) (reporting packingdensity values ranging from 0.66 to 0.95). Vacuum-deposited aluminumoxide films on cold substrates are generally amorphous while an acicularcrystalline structure appears at higher substrate temperatures. Id.

The degree of packing density can be easily controlled through the useof ion bombardment or plasma activation during deposition. Asdemonstrated in one study, packing density of electron-beam evaporatedaluminum oxide films can be controlled through oxygen ion bombardmentduring deposition. In this study, the index of refraction, and thereforethe film density, first rose and then decreased with increasing ioncurrent density for substrate temperatures between 70° C. and 250° C.See, Franzen, W., et al., “Study of Oxygen-Ion-Beam-Assisted EvaporatedAluminum Oxide Films,” Mat. Res. Soc. Symp. Proc., Vol. 29, pp. 825-30(1993). Similarly, the addition of plasma activation during filmdeposition has been shown to produce a glassy fracture and densermicrostructure than film deposition without plasma activation. See,Zywitzki, O., et al., “Effect of Plasma Activation on the PhaseTransformations of Aluminum Oxide,” Surface and Coatings Tech. 76-77,pp. 745-762 (1995).

The aluminum oxide layer 102 is a porous layer having a packing densityof less than 1. For one embodiment, the aluminum oxide layer 102 has apacking density of between approximately 0.65 and 0.999. For a furtherembodiment, the aluminum oxide layer 102 has a packing density ofbetween approximately 0.85 and 0.999.

The aluminum oxide layer 102 is doped, subsequent to deposition orformation, to improve the dielectric properties of the resultant film.In FIG. 1B, a dopant layer 106 is formed on the aluminum oxide layer102. The dopant layer 106 contains a dopant material. For oneembodiment, the dopant layer 106 contains silicon (Si). For additionalembodiments, the dopant layer 106 may contain zirconium (Zr), titanium(Ti) or hafnium (Hf). The dopant layer 106 fills pores 104 of thealuminum oxide layer 102 and covers the surface of the aluminum oxidelayer 102.

The dopant layer 106 may be formed by PVD or chemical vapor deposition(CVD) techniques as a blanket deposition. As one example, asilicon-containing dopant layer 106 may be formed by CVD using silane(SiH₄) or other suitable silicon precursor. For one embodiment, a dilutesilane feed, e.g., 2% silane in nitrogen (N₂), is pulsed into a reactionchamber for deposition of the dopant layer 106 on the aluminum oxidelayer 102. The dopant layer 106 is deposited to a thickness less than orequal to an average diameter of the pores 104 using a substratetemperature of approximately 300° C. to 350° C. This process is similarto the passivation of a copper substrate by silicide formation asprovided in Hymes, S., et al., “Passivation of Copper by SilicideFormation in Dilute Silane,” Mat. Res. Soc. Conf. Proc., ULSI-VII, pp.425-31 (1992). For a further embodiment, the dopant layer 106 isdeposited to a thickness of less than approximately 5 nm.

In FIG. 1C, excess dopant material is optionally removed from thesurface of the aluminum oxide layer 102. This leaves islands 107 ofdopant material, i.e., that material filling the pores 104, embedded inthe surface of the aluminum oxide layer 102. For one embodiment, removalof excess dopant involves exposing the surface of the dopant layer 106to a mild ion beam, such as a beam of argon (Ar) ions. Removal of excessdopant material can eliminate the series capacitance effects of twoadjacent dielectric layers.

For one embodiment, the aluminum oxide layer 106 has a packing densitysuch that the dopant material embedded in the surface of the aluminumoxide layer 102, e.g., the islands 107 of dopant material, constitutesapproximately 0.1% to 30% by weight of the doped aluminum oxide layer108. For a further embodiment, the aluminum oxide layer 106 has apacking density such that the dopant material embedded in the surface ofthe aluminum oxide layer 102 constitutes approximately 0.1% to 10% byweight of the doped aluminum oxide layer 108.

Whether or not the excess dopant material is removed, the dopantmaterial is subsequently treated to homogenize the doped aluminum oxidelayer 108. Such treatment of the dopant material can include oxidationor nitridation to convert the dopant material to its oxide or nitrideform appropriate to impart dielectric properties to the dopant material.

For one embodiment, the dopant material is oxidized by rapid thermalannealing in an oxidizing atmosphere, such as an oxygen-containingatmosphere. The oxygen-containing atmosphere should preferably containsufficient oxygen to oxidize all of the dopant material. For example,for a dopant layer 106 containing silicon, the oxygen-containingatmosphere should contain sufficient oxygen to convert all of thesilicon, i.e., the dopant layer 106 or the islands 107 of dopantmaterial, to silicon dioxide. For other embodiments, the treated dopantmaterial includes zirconium dioxide (ZrO₂), hafnium dioxide (HfO₂) ortitanium dioxide (TiO₂), formed by oxidation of zirconium, hafnium ortitanium dopant materials, respectively.

For another embodiment, the dopant material is nitrided by rapid thermalnitridation in a nitrogen-containing atmosphere. The nitrogen-containingatmosphere should preferably contain sufficient nitrogen to nitridateall of the dopant material. For example, for a dopant layer 106containing silicon, the nitrogen-containing atmosphere should containsufficient nitrogen to convert all of the silicon, i.e., the dopantlayer 106 or the islands 107 of dopant material, to silicon nitride(Si₃N₄).

FIG. 1D is a cross-sectional view of one deposition system 112 for usein forming an aluminum oxide layer 102 as described above. Thedeposition system 112 includes a chamber 114 for containing thesubstrate 100 under vacuum. A crucible 118 holds an aluminum or aluminasource 122. The source 122 is heated, e.g., by resistive heating orelectron-beam bombardment, to produce vaporized species 124 fordeposition on a surface of the substrate 100. If the vaporized species124 are aluminum atoms, they may be reacted with an oxygen-containingatmosphere within the chamber 114 to produce aluminum oxide.

An ion gun 126 may be included in the deposition system 112 to provideion beams 132 impinging on the surface of the substrate 100. The ionbeams 132 generally impinge on the surface of substrate 100 at someangle, e.g., approximately 20°. A gas inlet 128 provides an ion sourcefor the ion gun 126, e.g., oxygen or argon to produce oxygen ions andargon ions, respectively. For plasma activation of the vaporized species124, a plasma 134 is formed between the crucible 118 and the substrate100.

The doped aluminum oxide layer 108 may be used as a dielectric layer ina variety of integrated circuit devices subsequent to converting thedopant material to its dielectric form. Example uses include gatedielectric layers for field-effect transistors, intergate dielectriclayers for floating-gate transistors and capacitor dielectric layers.The doped aluminum oxide layer 108 differs from layers of aluminum oxidethat are doped during deposition in that the dopant material is notdispersed throughout the layer. The evaporation PVD techniquesfacilitate use of high-purity sources. The evaporation PVD techniquesfurther facilitate control over the degree of porosity, and thus thedopant level, of the resultant layer.

FIG. 2 is a cross-sectional view of a field-effect transistor having agate stack 245 overlying a substrate 200, a first source/drain region235 in the substrate 200 adjacent a first sidewall of the gate stack245, and a second source/drain region 240 in the substrate 200 adjacenta second sidewall of the gate stack 245. The gate stack 245 includes agate dielectric layer 205. The gate dielectric layer 205 contains adoped aluminum oxide layer in accordance with an embodiment of theinvention. Gate stack 245 further includes a conductor, often containinga conductively-doped polysilicon layer 210 overlying the gate dielectriclayer 205, a metal layer 220, and a conductive barrier layer 215interposed between the polysilicon layer 210 and the metal layer 220.Insulative cap layer 225 and sidewall spacers 230 insulate and protectthe gate stack 245 from other adjacent layers. The field-effecttransistor of FIG. 2 may be an access transistor of a DRAM memory cell,having the first source/drain region 235 coupled to a bit line and thesecond source/drain region 240 coupled to a cell capacitor.

FIG. 3 is a cross-sectional view of a floating-gate field effecttransistor, or simply a floating-gate transistor, having a gate stack345 overlying a substrate 300, a first source/drain region 335 in thesubstrate 300 adjacent a first sidewall of the gate stack 345, and asecond source/drain region 340 in the substrate 300 adjacent a secondsidewall of the gate stack 345. The gate stack 345 includes a gatedielectric layer 305. For one embodiment, the gate dielectric layer 305contains a doped aluminum oxide layer in accordance with an embodimentof the invention. Gate stack 345 further includes a floating-gate layer311, a control-gate layer 321 and an intergate dielectric layer 317interposed between the floating-gate layer 311 and the control-gatelayer 321. For one embodiment, the intergate dielectric layer 317contains a doped aluminum oxide layer in accordance with an embodimentof the invention.

Insulative cap layer 325 and sidewall spacers 330 insulate and protectthe gate stack 345 from other adjacent layers. The floating-gatetransistor of FIG. 3 may be a flash memory cell, having the firstsource/drain region 335 coupled to a bit line of a flash memory arrayand having at least the control-gate layer 321 coupled to a word line ofthe flash memory array. The second source/drain region 340 is generallycommonly coupled among all memory cells of the flash memory array or aportion of the flash memory array.

FIG. 4 is a cross-sectional view of a portion of a DRAM memory array.The memory array includes word lines 445 a as access transistorsoverlying the substrate 400. Word lines 445 b are formed overlyingisolation regions 495 and are coupled to access transistors for memorycells outside the plane of the drawing. Each memory cell of the DRAMmemory array includes an access transistor and a cell capacitor.

Each word line 445 a has a first source/drain region 435 coupled to abit line 485 through a bit-line contact 490. Each word line 445 afurther has a second source/drain region 440 coupled to a first plate455 of a cell capacitor, such as through a conductive plug 450. The cellcapacitor has a second plate 470 and a cell dielectric layer 465interposed between the first plate 455 and the second plate 470. Thesecond plate 470, or cell plate, is generally shared among all memorycells of the memory array or a portion of the memory array. Insulatinglayer 480 provides structural support to the cell capacitors as well aselectrical isolation of adjacent conductive layers.

For one embodiment, the cell dielectric layer 465 contains a dopedaluminum oxide layer in accordance with an embodiment of the invention.For another embodiment, the word lines 445 a contain a doped aluminumoxide gate dielectric layer in accordance with an embodiment of theinvention.

FIG. 5 is a simplified block diagram of an integrated circuit memorydevice 500 in accordance with an embodiment of the invention. The memorydevice 500 may include a DRAM device or a flash memory device. Thememory device 500 includes an array of memory cells 502, an addressdecoder 504, row access circuitry 506, column access circuitry 508,control circuitry 510, and Input/Output (I/O) circuitry 512. For a DRAMmemory device, the memory array 502 contains memory cells having anaccess transistor coupled between a bit line and a capacitor. For aflash memory device, the memory array 502 contains flash memory cellshaving a floating-gate transistor coupled to a bit line.

The memory device 500 can be coupled to a processor 514 or other memorycontroller for accessing the memory array 502. The memory device 500coupled to a processor 514 forms part of an electronic system. Someexamples of electronic systems include personal computers, peripheraldevices, wireless devices, digital cameras, personal digital assistants(PDAs) and audio recorders.

The memory device 500 receives control signals across control lines 516from the processor 514 to control access to the memory array 502. Accessto the memory array 502 is directed to one or more target memory cellsin response to address signals received across address lines 518. Onceaccessed in response to the control signals and the address signals,data is written to or read from the memory cells across DQ lines 520.

The memory cells of the memory array 502 are generally arranged in rowsand columns with a memory cell located at each intersection of a bitline and a word line. Those memory cells coupled to a single word lineare generally referred to as a row of memory cells while those memorycells coupled to a single bit line are generally referred to as a columnof memory cells. The array of memory cells 502 includes at least onememory cell having a gate dielectric layer, an intergate dielectriclayer or a capacitor dielectric layer in accordance with the invention.

It will be appreciated by those skilled in the art that additionalcircuitry and control signals can be provided, and that the memorydevice of FIG. 5 has been simplified to help focus on the invention. Itwill be understood that the above description of a memory device isintended to provide a general understanding of the memory and is not acomplete description of all the elements and features of a typicalmemory device.

As recognized by those skilled in the art, memory devices of the typedescribed herein are generally fabricated as an integrated circuitcontaining a variety of semiconductor devices. The integrated circuit issupported by a substrate. Integrated circuits are typically repeatedmultiple times on each substrate. The substrate is further processed toseparate the integrated circuits into dies as is well known in the art.

The foregoing figures were used to aid the understanding of theaccompanying text. However, the figures are not drawn to scale andrelative sizing of individual features and layers are not necessarilyindicative of the relative dimensions of such individual features orlayers in application. Accordingly, the drawings are not to be used fordimensional characterization.

CONCLUSION

Aluminum oxide has shown considerable promise as a dielectric materialfor integrated circuit devices. However, its porous nature leads todrawbacks in that the pores can adsorb water, thus resulting in adetrimental impact on the dielectric properties of the aluminum oxidematerial. The various embodiments of the invention involve a porousaluminum oxide layer having dopant material embedded in its pores andsubsequently converted to a dielectric form. The doped aluminum oxidelayer is formed sequentially to facilitate formation of a high-purityaluminum oxide layer and subsequently sealing its pores to impede wateradsorption. Doped aluminum oxide layers of various embodiments areespecially suited for use as gate dielectric layers, intergatedielectric layers and capacitor dielectric layers in various integratedcircuit devices.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.For example, other materials, shapes, deposition techniques and removaltechniques may be utilized with the invention. Accordingly, thisapplication is intended to cover any adaptations or variations of theinvention. It is manifestly intended that this invention be limited onlyby the following claims and equivalents thereof.

1. A capacitor, comprising: a first capacitor plate; a second capacitorplate; and a dielectric layer interposed between the first capacitorplate and the second capacitor plate, wherein the dielectric layerincludes an aluminum oxide layer and a second dielectric materialembedded in a surface of the aluminum oxide layer, wherein a dopantmaterial is embedded in the surface of the aluminum oxide layer after aformation of the aluminum oxide layer, thereby not dispersing the dopantmaterial throughout the aluminum oxide layer, and the dopant material issubsequently treated to form the second dielectric material, and whereinthe dopant material is selected from the group consisting of silicon,zirconium, hafnium and titanium.
 2. The capacitor of claim 1, whereinthe second dielectric material is a dielectric material selected fromthe group consisting of oxide forms of silicon, zirconium, hafnium andtitanium, and nitride forms of silicon.
 3. The capacitor of claim 1,wherein the second dielectric material is a dielectric material selectedfrom the group consisting of silicon dioxide, zirconium dioxide, hafniumdioxide, titanium dioxide and silicon nitride.
 4. The capacitor of claim1, wherein the aluminum oxide layer is formed by a method selected fromthe group consisting of thermal evaporation, electron-beam evaporationand ion-beam-assisted deposition.
 5. The capacitor of claim 4, wherein adegree of porosity of the aluminum oxide layer is controlled duringformation of the aluminum oxide layer using a method selected from thegroup consisting of ion bombardment and plasma activation.
 6. Thecapacitor of claim 1, wherein the aluminum oxide layer has a packingdensity between approximately 0.66 and 0.999.
 7. The capacitor of claim1, wherein the aluminum oxide layer has a packing density betweenapproximately 0.85 and 0.999.
 8. The capacitor of claim 1, wherein thedopant material constitutes approximately 0.1% to 30% by weight of thealuminum oxide layer.
 9. The capacitor of claim 1, wherein the dopantmaterial constitutes approximately 0.1% to 10% by weight of the aluminumoxide layer.
 10. The capacitor of claim 1, wherein the aluminum oxidelayer has a degree of porosity such that the dopant material embedded inthe surface of the aluminum oxide layer constitutes approximately 0.1%to 30% by weight of the aluminum oxide layer.
 11. The capacitor of claim1, wherein the aluminum oxide layer has a degree of porosity such thatthe dopant material embedded in the surface of the aluminum oxide layerconstitutes approximately 0.1% to 10% by weight of the aluminum oxidelayer.
 12. The capacitor of claim 2, wherein dopant material is formedby blanket depositing the dopant material on the surface of the aluminumoxide layer.
 13. The capacitor of claim 12, wherein excess dopantmaterial is removed from the surface of the aluminum oxide layer priorto treating the dopant material.
 14. The capacitor of claim 12, whereinthe second dielectric material contains silicon dioxide formed by achemical vapor deposition of silicon using dilute silane in nitrogen anda substrate temperature of approximately 300° C. to 350° C., followed byrapid thermal annealing the silicon in an oxygen-containing atmosphere.15. The capacitor of claim 12, wherein the dopant material is depositedto a thickness less than or equal to an average diameter of the pores.16. The capacitor of claim 1, wherein the capacitor is a cell capacitorof a memory cell of a dynamic random access memory device.
 17. Acapacitor, comprising: a first capacitor plate; a second capacitorplate; and a dielectric layer interposed between the first capacitorplate and the second capacitor plate, wherein the dielectric layerincludes: an aluminum oxide layer and a second dielectric materialembedded in a surface of the aluminum oxide layer; wherein a degree ofporosity of the aluminum oxide layer is controlled during formation ofthe aluminum oxide layer wherein a dopant material is embedded in thesurface of the aluminum oxide layer after a formation of the aluminumoxide layer, thereby not dispersing the dopant material throughout thealuminum oxide layer; wherein the dopant material is selected from thegroup consisting of silicon, zirconium, hafnium and titanium; andwherein the dopant material is subsequently treated to form the seconddielectric material selected from the group consisting of silicondioxide, zirconium dioxide, hafnium dioxide, titanium dioxide andsilicon nitride.
 18. The capacitor of claim 17, wherein the aluminumoxide layer is formed by a method selected from the group consisting ofthermal evaporation, electron-beam evaporation and ion-beam-assisteddeposition.
 19. The capacitor of claim 18, wherein the degree ofporosity of the aluminum oxide layer is controlled during formation ofthe aluminum oxide layer using a method selected from the groupconsisting of ion bombardment and plasma activation.
 20. The capacitorof claim 17, wherein the aluminum oxide layer has a degree of porositysuch that the dopant material embedded in the surface of the aluminumoxide layer constitutes approximately 0.1% to 30% by weight of thealuminum oxide layer.
 21. The capacitor of claim 17, wherein thealuminum oxide layer has a degree of porosity such that the dopantmaterial embedded in the surface of the aluminum oxide layer constitutesapproximately 0.1% to 10% by weight of the aluminum oxide layer.
 22. Thecapacitor of claim 17, wherein dopant material is formed by blanketdepositing the dopant material on the surface of the aluminum oxidelayer.
 23. The capacitor of claim 22, wherein excess dopant material isremoved from the surface of the aluminum oxide layer prior to treatingthe dopant material.
 24. The capacitor of claim 22, wherein the dopantmaterial is deposited to a thickness less than or equal to an averagediameter of the pores.
 25. The capacitor of claim 17, wherein thecapacitor is a cell capacitor of a memory cell of a dynamic randomaccess memory device.